Printed smart devices for anti-counterfeiting allowing precise identification with household equipment

Counterfeiting has become a serious global problem, causing worldwide losses and disrupting the normal order of society. Physical unclonable functions are promising hardware-based cryptographic primitives, especially those generated by chemical processes showing a massive challenge-response pair space. However, current chemical-based physical unclonable function devices typically require complex fabrication processes or sophisticated characterization methods with only binary (bit) keys, limiting their practical applications and security properties. Here, we report a flexible laser printing method to synthesize unclonable electronics with high randomness, uniqueness, and repeatability. Hexadecimal resistive keys and binary optical keys can be obtained by the challenge with an ohmmeter and an optical microscope. These readout methods not only make the identification process available to general end users without professional expertise, but also guarantee device complexity and data capacity. An adopted open-source deep learning model guarantees precise identification with high reliability. The electrodes and connection wires are directly printed during laser writing, which allows electronics with different structures to be realized through free design. Meanwhile, the electronics exhibit excellent mechanical and thermal stability. The high physical unclonable function performance and the widely accessible readout methods, together with the flexibility and stability, make this synthesis strategy extremely attractive for practical applications.


Supplementary
Spots generated with lower laser power (a) tend to be washed away more easily during the first spin-coating step in contrast to those with higher laser power (b, c).Therefore, less micro-holes will be observed after annealing.

Figure S2 Figure S4 Figure S6 Figure S7 Figure S11
Figure S2 Synthesis process of a PUF device 4 Figure S3 Tuning the micro-hole pattern by the printing parameters during the generation of the polymer spot array 5 Figure S4 Height map and profile of the thicker hematite film 6 Figure S5 Resistance values of the electrodes obtained with different laser carbonization parameters 7 Figure S6 PUF electronics synthesized by carbonization of styrene acrylic copolymer (s-LEC) under different laser scanning parameters 8 Figure S7 PUF electronics synthesized by carbonization of PVP under different laser scanning parameters 9 Figure S8 PUF electronics synthesized by carbonization of PVA under different laser scanning parameters Figure S9 PUF electronics synthesized with different carbonization repetitions Figure S10 Device uniqueness of the PUF patterns were characterized by inter-device Hamming distance Figure S11 Electrode resistance of the samples with different writing angles in reference to the direction of connection wires Figure S12 Characterization of device uniqueness, false authentication, and authentication error of the PUF patterns by LoFTR Figure S13 Quantitative analyses of the surface roughness (root-mean-square (RMS) height standard deviation) of the electrode areas before and after the treatments Figure S14 Semi-automatic resistance measurement setup TableS1Comparison between the proposed PUF device and recently reported PUFs from the literature

Figure S1 .
Figure S1.Process of generating a polymer spot pattern by laser-induced forward transfer (LIFT).(a) A donor glass substrate, covered with a (hematite) nanofilm laser absorber (~400 nm), is spin coated with a thin polymer (e.g., polystyrene) film of ~200 nm.(b) The donor slide is placed onto a glass acceptor substrate (future PUF device) and a polymer spot pattern is transferred.

Figure S2 .
Figure S2.Synthesis process of a PUF device.A polymer spot array is generated on a glass substrate by LIFT.During the first spin-coating step, an iron nitrite solution randomly washes away some or parts of the polymer spots.After annealing at 500 °C for 10 min, a hematite nanofilm with micro-hole patterns is obtained.This (inhomogeneous) hematite layer functions as a laser absorber to carbonize the polymer films on top of it under laser irradiation.Then, the whole area is brushed with colloidal graphite, which is washed away together with the uncarbonized polymer.

Figure S3 .
Figure S3.The micro-hole pattern can be tuned by the printing parameters during the generation of the polymer spot array.Spot patterns with (a) low (50 % = 55 mW), (b) medium (60 % = 63 mW), and (c) higher (80 % = 95 mW) laser power (all 500 µs irradiation per spot).Spots generated with lower laser power (a) tend to be washed away more easily during the first spin-coating step in contrast to those with higher laser power (b, c).Therefore, less micro-holes will be observed after annealing.

Figure S4 .
Figure S4.Height map and profile of the thicker hematite film.

Figure S6 .
Figure S6.PUF electronics synthesized by carbonization of styrene acrylic copolymer (S-LEC) under different laser scanning parameters.Data shown as average of n = 3 measurements with standard deviation.

Figure S7 .
Figure S7.PUF electronics synthesized by carbonization of PVP under different laser scanning parameters.Data shown as average of n = 3 measurements with standard deviation.

Figure S8 .
Figure S8.PUF electronics synthesized by carbonization of PVA under different laser scanning parameters.Data shown as average of n = 3 measurements with standard deviation.

Figure S9 .
Figure S9.PUF electronics synthesized with different carbonization repetitions.When repeating the laser carbonization once (step 3 is only repeated for the electrode areas, not for the connection wires), the resistance tends to be decreased and more stable.Data shown as average of n = 3 measurements with standard deviation.

Figure S10 .
Figure S10.Device uniqueness of the PUF patterns were characterized by inter-device Hamming distance (HD).The readout reproducibility of the PUF patterns was characterized by the intra-device HD, where each PUF pattern was scanned three times.

Figure S11 .
Figure S11.Electrode resistance (1# to 8#) of the samples with different writing angles in reference to the direction of connection wires.Each sample is measured three times.The mean value and standard error are shown in the figures.

Figure S12 .
Figure S12.Characterization of device uniqueness, false authentication, and authentication error of the PUF patterns by LoFTR.(a) Device uniqueness of the micro-hole patterns were characterized by inter-device LoFTR similarity.The readout reproducibility of the micro-hole patterns was characterized by the intra-device LoFTR similarity, where each PUF pattern was scanned twice.(b) Cumulative distribution functions, showing the probabilities of false authentication (FA) and authentication error (AE) as a function of decision threshold.Details about LoFTR similarity calculations can be found in the Methods part of the manuscript.

Figure S14 .
Figure S14.Semi-automatic resistance measurement setup.Nine metal pins are arranged in a 3 x 3 rectangle to fit the contact electrodes of our standard PUF devices.The pins are spring-loaded and a hand gear allows them to be moved up and down for quick contact.A window in the table, directly below the pins with an LED, allows for easy repositioning and alignment of the PUF on the table.A rotary selector switch allows manual selection of the circuit, which is connected to the ohmmeter.

Table S1 . Comparison between the proposed PUF device and recently reported PUFs from the literature. Table S2. PUF parameters for fluorescence and topography characterization.
Calculated values are the average with standard deviation.